Interpretive Summary: The reuse of treated wastewater for groundwater recharge is an effective way to provide advanced treatment and water storage in the desert southwest. Pharmaceutically active compounds (PhAC’s) found in treated effluent, have been identified as a potential problem for use of this water. The accumulation of four PhAC’s was investigated at a groundwater recharge facility. Two PhAC’s, ibuprofen and the antibiotic lincomycin, were shown not to accumulate over a three year period while, caffeine and the anti-seizure medication carbamazepine were observed to accumulate over the same three years. However, the total accumulated carbamazepine and caffeine was very small (1 part per billion and 4 parts per billion respectively).

Technical Abstract:
The reuse of treated wastewater for groundwater recharge is an effective way to provide advanced treatment and water storage in the desert southwest. Contaminants such as human drugs, found in treated effluent, have been identified as a potential problem for use of this water. The town of Gilbert, Arizona maintains a 28.3 ha facility designed to recharge 15 150 m3 day-1 through recharge basins constructed on native soil previously used for agricultural production. On an annual basis, the facility maintains an infiltration rate of more than 5 cm day-1 resulting in the potential for leaching of pharmaceutical compounds to groundwater. One 4 ha basin was selected for spatial sampling to a depth of 1.5 m for four pharmaceutically active compounds (PhAC’s). The compounds chosen were the anti-epileptic drug carbamazepine, the anti-microbial lincomycin, the analgesic ibuprofen, and the stimulant caffeine. Soils were extracted using pressurized liquid extraction followed by analysis using LC-MS-MS. The concentration of ibuprofen was below detection limits in all samples with no accumulation over three years. Similarly, lincomycin exhibited no net accumulation from year to year but had significantly higher concentrations in 0-5 cm samples than samples collected from >10 cm. Carbamazepine had the lowest concentration at 0-5 cm (0.18 ng g-soil-1) providing evidence that there is potential degradation of carbamazepine in surface soils. Carbamazepine also exhibited significant accumulation from year to year. Caffeine exhibited net accumulation from 2009 to 2011 and had higher concentrations in surface samples. The accumulation of PhAC’s in the soil beneath recharge basins indicates that PhAC’s are being removed from the infiltrating water and that in the case of ibuprofen and lincomycin the treatment is sustainable due to the lack of accumulation. In the case of carbamazepine and caffeine further investigations are needed to determine possible management and environmental conditions that could prevent their accumulation.